A major consideration in the comfort of a garment is its ability to maintain a balance between heat production and heat loss. The loss of heat through clothing may occur through direct dry heat loss or by moisture evaporation. In respect to the latter, the moisture vapor transmission rate of the material utilized in forming the garment is generally related to the breathability of the material. Breathability is the ability to diffuse moisture/water vapor through a film or garment. In addition to this property, there are many applications requiring that the material used in preparing the garment be impermeable to a liquid. Such applications include diaper back sheets, sanitary napkins, medical protective garments, surgical incise drapes, transdermal patches, wound care bandages and dressings, intravenous site dressings and ostomy site dressings, among others.
Films which are permeable to water vapor and are porous but yet are intended to be impermeable to a liquid are described in U.S. Pat. Nos. 4,626,252 and 5,073,316. As disclosed, a porous film is obtained by mixing a polyolefin resin, an inorganic filler and a plasticizer; forming a film from the mixture; and uniaxially or biaxially stretching the film. However, a drawback of this prior art is that during the process of stretching the film to render them permeable to water vapor, certain disadvantages arise, such as reduced mechanical properties and/or microvoids (holes that may permit viral/disease transmission).
The use of certain inert non-microporous inorganic fillers are disclosed in S. S. Steingiser, S. P. Nemphos, and M. Salame, "Encyclopedia of Chemical Technology," 3rd Edition, 2d, H. F. Mark et al., Wiley Interscience, New York, 1978, Vol. 3, p. 482, and J. Crank and G. S. Park, "Diffusion in Polymers," Academic Press, New York, 1968, pp. 200-203).
Thus, it would be very desirable to produce continuous, non-porous films that have improved moisture vapor transmission rates (MVTR) but that are impermeable to liquids, such as blood, without any necessity for stretching of the film.